java生成随机字符串（密码）包含字母，数字，a-z,A-Z,0-9

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import java.util.Random;
import java.util.UUID;

/**
 * 生产指定长度随机字符串a-z,A-Z,0-9
 * @author happyqing
 * @since 2016.5.30
 */
public class RandomString {

	/**
	 * 获取随机字符串 a-z,A-Z,0-9
	 * @param length	长度
	 * @return
	 */
	public static String getRandomString(int length) {
		String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
		Random random = new Random();
		StringBuffer sb = new StringBuffer();

		for (int i = 0; i < length; ++i) {
			//int number = random.nextInt(62);// [0,62)
			sb.append(str.charAt(random.nextInt(62)));
		}
		return sb.toString();
	}
	
	/**
	 * JAVA获得0-9,a-z,A-Z范围的随机数
	 * 
	 * @param length
	 *            随机数长度
	 * @return String
	 */
	public static String getRandomChar(int length) {
		char[] chr = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
				'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 
				'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };
		Random random = new Random();
		StringBuffer buffer = new StringBuffer();
		for (int i = 0; i < length; i++) {
			buffer.append(chr[random.nextInt(62)]);
		}
		return buffer.toString();
	}
	
	/**
	 * 获取随机字符串 a-z
	 * @param length	长度
	 * @return
	 */
	public static String getLowerLetter(int length) {
		String str = "abcdefghijklmnopqrstuvwxyz";
		Random random = new Random();
		StringBuffer sb = new StringBuffer();
		for (int i = 0; i < length; ++i) {
			sb.append(str.charAt(random.nextInt(26)));
		}
		return sb.toString();
	}
	
	/**
	 * 获取随机字符串 0-9
	 * @param length	长度
	 * @return
	 */
	public static String getNumber(int length) {
		String str = "0123456789";
		Random random = new Random();
		StringBuffer sb = new StringBuffer();
		for (int i = 0; i < length; ++i) {
			sb.append(str.charAt(random.nextInt(10)));
		}
		return sb.toString();
	}
	
	/**
	 * 获取随机字符串 0-9,a-z,0-9
	 * 有两遍0-9，增加数字概率
	 * @param length	长度
	 * @return
	 */
	public static String getLowerLetterNumber(int length) {
		String str = "0123456789abcdefghijklmnopqrstuvwxyz0123456789";
		Random random = new Random();
		StringBuffer sb = new StringBuffer();
		for (int i = 0; i < length; ++i) {
			sb.append(str.charAt(random.nextInt(46)));
		}
		return sb.toString();
	}
	
	/**
	 * 获取随机密码，lLength位小写英文+nLength位数字
	 * @param lLength	字母长度
	 * @param nLength	数字长度
	 * @return
	 */
	public static String getPasswordSimple(int lLength, int nLength) {
		return getLowerLetter(lLength)+getNumber(nLength);
	}
	
	/**
	 * 获取随机密码，包含英文和数字
	 * @param length 密码长度
	 * @return
	 */
	public static String getPasswordComplex(int length) {
		String password;
		while(true){
			password = getLowerLetterNumber(6);
			//必须包含字母和数字
            if (password.matches("(?![0-9]+$)(?![a-zA-Z]+$)[0-9A-Za-z]{6,20}")) {
                return password;
            }
        }
	}

	public static void main(String[] args) {
//		System.out.println(getRandomString(32));
//		System.out.println(getRandomChar(32));
//		//UUID
//		String uuid = UUID.randomUUID().toString().replaceAll("-", "");
//		System.out.println(uuid);
		
		System.out.println(getPasswordSimple(1,5));
		System.out.println(getPasswordComplex(6));
	}
}